Cathode for magnetrons



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H. G. ANDERSQN CATHODE FOR MAGNETRONS Original Filed Nov. 7. 3.944

Patented Sept. 6, 1949 UNITED Afs'l'flrrss Pars-NT OFFICE CATHODE FOR MAGNETRONS Homer G. Anderson, .Newtonvilla Mass., assigner to `Raytheon .Manufacturing Company, Newton, Mass., a. corporation of Delaware Original applicationfNovemher 7, 1944, Serial No. 562,334. Divided and this application August 20, 1947, 4Serial No. 769,705

it has been found that interaction between the magnetic field established by the current owing in the cathode heater wire and the magnetic eld established 'transversely of the discharge path between the cathode and anode is detrimental to the ,proper operation oi' the device.

It is, therefore, the main object of this invention to eliminate the aforesaid interaction between the aforesaid magnetic fields.

This object and such others as may hereinafter vappear will be vbest understood from the following description, taken in connection with the accompanying drawing of one embodiment of the invention herein presented for illustrativepurposes.

In the drawing:

Fig. 1 is a vertical section Vthrougl'i an electrondischarge device embodying one illustrative embodiment of the invention;

Fig. 2 is a cross-section online 2-2 oflllig. 1;

Fig. 3 is an enlarged vertical section .of the cathode on line S- of Fig. 4, .showing the connection of the upper lead-in conductor to the upper end of the rod supporting the heater wire and to the protective disk between the upper end of the cathode and the top cap of the device; it also shows the heater wire in elevation; .and

Fig. 4. is a cross-section on line 4-'4 .of Fig. 3, showing the connection .of the lower lead-in conductor to the protective disk between the bottom cap of the device and thelower end of the cathode.

The intention is herein illustrativelyshown and -described in its application. to that ytype of electron-discharge device known as a magnetron.

The illustrative Aembodimentol .the present 'invention shown comprises a cylindrical envelope v2, hermetically sealed at both endsby caps 4 and B. Said envelope and caps may and preferably will be made of copper. Upon the inner .surface of said envelope there is provided a central, circular projection 8 to which are soldered a plurality of suitably spaced, radially disposed plates l'll, the inner ends of which constitute anode faces. "Said plates lll will preferably be stamped from a sheet of highly conductive copper. Said anode faces cooperate with a cathode l2 supported substantially centrally of said anode faces, said cathode being preferably of the indirectly-heated, thermionic type, and comprising a conductive sleeve I4 'of nickel or other suitable conductive material coated with a coating of barium and strontium oxide or other suitable electromemisslve material.

The cathode l2 contains `a helically wound insulated heater wire I6 (see Fig. 3) supported by a conductive rod Ill, the Opposite ends of which are mounted in insulating washers 20, 24 in the opposits ends respectively of said sleeve i4. In accordance with the present invention said helically Wound heater wire l5 is wound clockwise throughout a part of its length and contra-clockwise throughout another portion of its length (see Fig. 3). Herein the Winding in one direction is equal to that in the opposite direction. This serves to neutralize the objectionable eiect of the magnetic field generated by the heater wire, by causing it to be exerted in one direction by one half of the wire and in the opposite direction by the other half so that diversion of the magnetic eld generated by the two pole pieces 'l2 and 'lll from its correct di rection and displacement of said heating wire are avoided` Herein the upper end of said heater wire is electrically connected to said supporting rod l 8, the other end of said'heater wire being electrically connected to the conductive cathode sleeve i4.

A lead-.in conductor 26 is sealed through a glass seal 28 mounted at the outer end of a conducting pipe 3R 'which extends through the wall of said envelope 2 and is hermetically secured therein adjacent the lower end thereof. A second lead-in conductor 32 is sealed through a similar glass seal Blmounted at'the outer end of a conducting pipe 3B, 'also hermetically secured in the wall of said envelope 2 at the upper end thereof.

Light, protective shields 38 and eli, respectively,

, of `tanta-lum or other suitable material are provided between the upper end of the cathode l2 -and the envelope cap 4, and between the lower 'end 'of said cathode l2 and the envelope cap 5. These shields prevent electron beams from being projected outwardly from said cathode toward said two envelope caps Il and 6. The edges of the thin shields heretofore used for this purpose were rough and relatively sharp, which were liable to cause sparking. The present invention contemr plates the provision of means for preventing such sparking. In accordance with the present invenu tion this is conveniently accomplished by welding .a metal ring 42 to the marginal portion of one side of the shield substantially as shown in Fig. .3., thus vincreasing the thickness of the .edge surface. Said ring 42 also serves the further useful purpose of reinforcing the thin shield and rendering it more rigid.

In the illustrative embodiment of the .invention shown in the drawing, the lead-in conductor 32 is connected to said shield 33 by a bracket or support consisting of a conductive wire bent back upon itself at 44 (see Fig. 2) so as to form two substantially parallel arms 4B, each presenting a U-shaped formation 48 and a lesser U-shaped formation 50, the latter also substantially parallel to each other but in planes at right angles to the plane of the U-shaped formations 48, and between the latter and the bend 44. The free ends of the two arms 46 are welded to the lead-in conductor 32 and said arms are also Welded at the points 52 (see Fig. 2) to the reinforced edge of the shieldv on the underside of the latter, the bend 44 of said arms being welded to the opposite edge of said shield 54 (see Fig. 3) The lesser U-shaped formations 50 are welded to opposite sides of the upper end of the aforesaid heater wire i6 supporting rod I8 projecting from the upper end of the. cathode I2, thus electrically connecting said leadin wire 32 to saidheater wire I6. The lesser U- shaped formations 50 provide the required spacing of said wire arms 45 and said shield 38 from the top of the cathode I2.

The lower shield 40 is electrically connected to the cathode sleeve I4 by metal supports 56 welded to the lower edge of said cathode and to the reinforced edge of said shield 4|), said shield being in turn connected to the lead-in conductor 26 by two wire arms 58 and @il having one end welded to said lead-in conductor and the other end welded to the reinforced edge of said shield 40. These wire arms are provided with substantially U-shaped formations 62. These U-shaped formations 62 and the above-mentioned U-shaped formations 48 pro-vide for the extension or contraction of the wire connections between said shields 38 and 40 with their respective lead-in conductors as may be necessary to span the distance separating said shields from their corresponding lead-in conductors, should said distances vary.

The above-described connections between saidl lead-in conductor 32 and shield 38 and the upper end of the heater-wire supporting rod I8, on the one hand, and the lead-in conductor 26 with said shield 4! and the cathode I2, on the other hand, provide the necessary electrical connections of said two lead-in conductors with said heater wire and with the cathode, it having already been stated abo-ve that one end of said heater wire IB is electrically connected to said rod I8 and the other end of said heater wire is connected to said cathode sleeve i4.

A coupling loop 64 extends into the space between two of said plates IIJ, one end of said loop being connected to the inner end of a conducting pipe |66 hermetically sealed through the wall of the envelope 2, substantially midway between the ends thereof, the other end of said loop being connected to a :conductor 68 extending through said pipe B and sealed through a glass seal 'I0 at the outer end of said pipe t6. An additional conducting pipe, not shown, may be electrically connected to said pipe E5 to form with said conductor 68 a concentric line through which the high frequency oscillations generated by the device when it is energized and placed between magnetic poles 12 and 'I4 may be conducted to a suitable utilizing circuit.

The firm support for the shield provided by welding the wire support to the shield at a plurality of points, for example, three suitably spaced points 52, 52 and 54, precludes any buckling, bending, tilting or other displacement of said shield from any cause.

As already pointed out, the shields of tantalum or any other suitable material may be used. For some cases nickel is particularly desirable, but, owing to its liability to distortion in a magnetic eld, shields of this metal have heretofore not proven very satisfactory. The rm support afforded the shields by the present invention, however, has overcome this difculty and made the use of nickel shields not only perfectly feasible but desirable in certain cases.

The above-described connections also, While affording a sturdy and reliable support for the cathode by said lead-in conductors, do not objectionably affect'the temperature of the cathode, for while a certain amount of heat will be withdrawn from the cathode by the shields, the amount so withdrawn in the present instance is an advantage, it being neither too little nor too much,

The present invention enables shields 38 and 40, and the wire supports for the latter, to be assembled and Welded in their proper positions to the cathode structure before the cathode is placed in the tube. The operator can thus make sure that the shields and other parts are correctly assembled and properly positioned before placing the assembly in the tube. The welding of the free ends of the wire supports to the ends of the lead-in wires is all that remains to be done and this can be accomplished without any risk of disturbing the assembly in the tube. The shields are supported in such manner that any change from the position in which they have been adjusted before being placed in the tube is practically impossible, whether by magnetic attraction or any other causes. The same applies to the heater wire, the winding of which in opposite directions neu-tralizes'any effect the magnetic field created by said wire might have upon that of said pole pieces and precludes any displacement of said heating wire by magnetic attraction by said pole pieces.

It will be noted that the coils of the resilient heater wire are in close contact with the interior lateral wall of the cathode. It will also be noted that the last coil of the closely coiled wire at one end rests against the disk 2I welded to the inner surface of the cathode and carrying the ribbons 23 that hold the insulating washer 24 in place, and that the last coil of said heater wire at the other end of the coiled wire rests against the disk 55 welded to the inner surface of the cathode. The closely coiled heater wire I6 is thus braced both longitudinally and transversely within the cathode and cannot be displaced Whatever the position of the cathode may be, whether vertical or horizontal, and the coils of said heater wire are distributed uniformly throughout the length of the cathode, thus ensuring even heating of the cathode throughout its length.

Wherever the term a plurality is used, it is to be construed as meaning two or more.

I am aware that the present invention can be embodied in other specific forms Without departing from the spirit or essential attributes there- 65 of, and I therefore desire the present description to be considered in all respects as illustrative and not restrictive, reference being had to the appended claims rather than to the aforesaid description to indicate the scope of the invention.

This application is a division of my Patent No. 2,439,786, published April 20, 1948.

What is claimed is:

1. An electron discharge device of the magnetron type, comprising: a cathode structure; 75 an anode structure, incorporating a cavity resonator, spaced from said cathode structure; and means adjacent said cathode and anode structures for establishing a magnetic field in a direction transverse to the discharge path therebetween; said cathode structure including a conductive sleeve provided with with an electronemissive coating; and a heater wire mounted in said sleeve, said heater wire being in the iorrn of a helix coiled in one direction throughout a portion of its length and in the opposite direction throughout another portion of its length.

2. An electron discharge device of the magnetron type, comprising: a cathode structure; an anode structure, incorporating a, cavity rescnator, spaced from said cathode structure; and means adjacent said cathode and anode structures for establishing a magnetic eld in a direction transverse to the discharge path therebe- REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,790,286 Sperti et al Jan. 27, 1931 2,130,124 Fritz Sept. 13, 1938 2,304,186 Litton Dec. 8, 1942 

